The future of the North Slope may increasingly look like this BP facility at Prudhoe Bay, where crude gets processed before being sent through the Trans-Alaska Pipeline. The largest petroleum field ever discovered in North America, Prudhoe peaked in 1987 with an output of 1.6 million barrels a day. Now production has fallen to a quarter of that figure. Hoping to stem this loss, the industry is expanding west into the unprotected wilderness of the National Petroleum Reserve-Alaska.